The purpose of this study is to compare therapeutic efficacy of topical Exorex which is a coal tar based emulsion for the treatment of psoriasis with a moisturizing cream (Eucerin cream), in a single blinded fashion. Expected outcome: only Exorex will be effective for treating psoriasis. This study plans to recruit 25 volunteers who are diagnosed with chronic plaque psoriasis. Study subjects will be male or females between the ages of 18-90. Patient's lesions will receive treatment with Eucerin cream or Exorex and Exorex PSE cream 2X per day for 4 months.